U.S. patent application number 11/671375 was filed with the patent office on 2007-06-07 for method and system for deposition tuning in an epitaxial film growth apparatus.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Wolfgang R. Aderhold, Ali Zojaji.
Application Number | 20070128780 11/671375 |
Document ID | / |
Family ID | 37056742 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070128780 |
Kind Code |
A1 |
Aderhold; Wolfgang R. ; et
al. |
June 7, 2007 |
METHOD AND SYSTEM FOR DEPOSITION TUNING IN AN EPITAXIAL FILM GROWTH
APPARATUS
Abstract
A method of calculating a process parameter for a deposition of
an epitaxial layer on a substrate. The method includes the steps of
measuring an effect of the process parameter on a thickness of the
epitaxial layer to determine a gain curve for the process
parameter, and calculating, using the gain curve, a value for the
process parameter to achieve a target thickness of the epitaxial
layer. The value is calculated to minimize deviations from the
target thickness in the layer. Also, a substrate processing system
comprising that includes a processor to calculate a value for the
process parameter to achieve a substantially uniform epitaxial
layer of a target thickness on the substrate, where the value is
calculated using a gain curve derived from measurements of layer
uniformity as a function of the value of the process parameter.
Inventors: |
Aderhold; Wolfgang R.;
(Cupertino, CA) ; Zojaji; Ali; (Santa Clara,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW LLP / AMAT
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
37056742 |
Appl. No.: |
11/671375 |
Filed: |
February 5, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11178973 |
Jul 11, 2005 |
7195934 |
|
|
11671375 |
Feb 5, 2007 |
|
|
|
Current U.S.
Class: |
438/180 ;
117/200 |
Current CPC
Class: |
C30B 25/02 20130101;
C23C 16/52 20130101; Y10T 117/10 20150115; C30B 25/165 20130101;
C30B 23/02 20130101 |
Class at
Publication: |
438/180 ;
117/200 |
International
Class: |
H01L 21/338 20060101
H01L021/338; C30B 11/00 20060101 C30B011/00 |
Claims
1. A substrate processing system comprising: a chamber; a substrate
holder, located within the chamber, to hold a substrate; a
precursor delivery system to introduce one or more precursors into
the chamber; a heating system to heat the substrate; and a
controller to control a process parameter in the precursor delivery
system or the heating system; and a processor to calculate a value
for the process parameter to achieve a substantially uniform
epitaxial layer of a target thickness on the substrate, wherein the
value is calculated using a gain curve derived from measurements of
layer uniformity as a function of the value of the process
parameter.
2. The substrate processing system of claim 1, wherein the heating
system comprises a plurality of lamps.
3. The substrate processing system of claim 2, wherein the lamps
are spatially distributed into a plurality of zones comprising an
outer zone, an inner zone, a lower zone, and an upper zone.
4. The substrate processing system of claim 3, wherein the process
parameter comprises an inner zone to outer zone power ratio.
5. The substrate processing system of claim 3, wherein the process
parameter comprises a lower zone to upper zone power ratio.
6. The substrate processing system of claim 1, wherein the
epitaxial layer comprises a SiGe layer.
7. The substrate processing system of claim 1, wherein the
substrate is a 300 mm silicon wafer.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/178,973, entitled "METHOD AND SYSTEM FOR DEPOSITION
TUNING IN AN EPITAXIAL FILM GROWTH APPARATUS," filed Jul. 11, 2005,
the entire disclosure of which is incorporated herein by reference
for all purposes.
BACKGROUND OF THE INVENTION
[0002] Modern processes for manufacturing semiconductor devices
require precise adjustment of many process parameters to achieve
high levels of device performance, product yield, and overall
product quality. For processes that include the formation of
semiconductive layers on substrates with epitaxial film growth,
numerous process parameters have to be carefully controlled,
including the substrate temperature, the pressures and flow rates
precursor materials, the formation time, and the distribution of
power among the heating elements surrounding the substrate, among
other process parameters.
[0003] Current trends in CMOS technology are favoring processes
that can produce increasingly thin layers (e.g., dielectric layers
only 60-80 .ANG. thick or less), and films with increasing
complexity. For example, conventional BiCMOS devices, using
single-element silicon (Si) films, are being displaced by
two-element, silicon-germanium (SiGe) films that have superior
qualities in logic and DRAM devices. As the sizes of these devices
continue to shrink, the uniformity of the film thickness and
composition across the substrate becomes increasingly important.
Maintaining a high level of uniformity is made even more
challenging due to the increasing sizes of the substrates, with the
standard substrate wafer diameter moving from 200 mm to 300 mm, and
beyond.
[0004] In many conventional semiconductor manufacturing process,
including epitaxial film growth processes ("EPI processes"),
process parameters can be manually adjusted to make films with the
requisite uniformity of film thickness and composition. In EPI
processes for making alloy films (e.g., SiGe films), especially
doped alloy films, the sensitivity of several process parameters on
film quality is increased, making it more difficult to tune these
parameters by hand. The increased sensitivity makes manual control
of semiconductor film growth processes much more difficult, if not
impossible.
[0005] There is also increasing complexity in the relationship
between process parameters and the qualities of the manufactured
film layer. Increasingly, the interdependencies of multiple process
parameters on a property of the layer make it more difficult to
find optimum values for the parameters to achieve a target value
for the property. For example, in an EPI process trying to achieve
a target thickness uniformity of a film layer across the substrate,
the interdependencies of the power ratios between inner/outer and
upper/lower substrate heating elements have to be understood. Only
with this understanding can the process operator set the parameters
to values that result in a sufficiently uniform thickness of the
deposited layer. Moreover, the interdependence of the parameters
make determining the parameter values much more difficult than if
the effects of each parameter on thickness uniformity were
completely independent.
[0006] Thus, there is a need for systems and methods of tuning
process parameters in semiconductor film growth processes that
reduce or eliminate the manual adjustment of the process
parameters. There is also a need for systems and methods to
determine values of interdependent process parameters for making a
film layer with the desired properties. These and other needs for
semiconductor film making systems and processes are addressed by
the present invention.
BRIEF SUMMARY OF THE INVENTION
[0007] Embodiments of the invention include a method of calculating
a process parameter for a deposition of an epitaxial layer on a
substrate. The method includes the steps of measuring an effect of
the process parameter on a thickness of the epitaxial layer to
determine a gain curve for the process parameter, and calculating,
using the gain curve, a value for the process parameter to achieve
a target thickness of the epitaxial layer. The value is calculated
to minimize deviations from the target thickness in the layer.
[0008] Embodiments of the invention also include a method of
calculating process parameters for a deposition of an epitaxial
layer. The method includes the steps of determining a first gain
equation comprising a first relationship between a first process
parameter and a thickness of the epitaxial layer, and determining a
second gain equation comprising a second relationship between a
second process parameter and the thickness of the epitaxial layer.
The method also includes calculating, using the first and second
gain equations, values for the first and second process parameters
to achieve the target thickness. The values are calculated to give
a uniform distribution of a component of the epitaxial layer.
[0009] Embodiments of the invention further relate to a substrate
processing system. The system may include a chamber, a substrate
holder, located within the chamber, to hold a substrate, a
precursor delivery system to introduce one or more precursors into
the chamber, a heating system to heat the substrate, and a
controller to control a process parameter in the precursor delivery
system or the heating system. The system may also include a
processor to calculate a value for the process parameter to achieve
a substantially uniform epitaxial layer of a target thickness on
the substrate. The value is calculated using a gain curve derived
from measurements of layer uniformity as a function of the value of
the process parameter.
[0010] Another embodiment of the invention relates to a system to
calculate a process parameter for a deposition of an epitaxial
layer on a substrate. The system may include a processor arranged
to obtain a value for the process parameter to achieve a target
thickness of the epitaxial layer. The value for the process
parameter may be obtained by measuring an effect of the process
parameter on a thickness of the epitaxial layer to determine a gain
curve for the process parameter, and calculating, using the gain
curve, a value for the process parameter to achieve a target
thickness of the epitaxial layer. The value for the process
parameter may be calculated to minimize deviations from the target
thickness in the layer.
[0011] Additional embodiments of the invention include methods of
setting a process parameter for a deposition of an epitaxial layer
on a substrate. The methods include measuring an effect of a
process parameter on a concentration distribution of a material in
the epitaxial layer to determine an effect profile for the process
parameter, and calculating, using the effect profile, a value for
the process parameter to achieve a target concentration profile of
the material in the epitaxial layer. The value of the process
parameter is calculated to minimize deviations from the target
concentration profile in the layer.
[0012] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the invention. The features and
advantages of the invention may be realized and attained by means
of the instrumentalities, combinations, and methods described in
the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is a flowchart showing methods of determining a
process parameter for the formation of an epitaxial film layer
according to embodiments of the invention;
[0014] FIG. 1B is a flowchart showing methods of determining a
first and second process parameter for formation of an epitaxial
film layer according to embodiments of the invention;
[0015] FIG. 1C is a flowchart showing methods of setting a process
parameter for the formation of an epitaxial film layer according to
additional embodiments of the invention;
[0016] FIGS. 2A-B shows aspects of a substrate processing system
according to embodiments of the invention;
[0017] FIGS. 3A-B show film layer thickness profiles across
substrate wafers after varying two interdependent process
parameters; and
[0018] FIG. 4 shows the thickness uniformity results from tuning
the process parameters; and
[0019] FIG. 5 shows the thickness uniformity results from tuning
the process parameters with the aid of the Epi process tuning
tool.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Methods and systems are described for tuning parameters in
an epitaxial film growth process in order to achieve films with a
desired thickness uniformity and/or compositional distribution.
Tunable process parameters include power settings for heating
elements in the various substrate heating zones of the process
chamber, and partial pressures and flow rate settings of the
process gases used in the chamber, among other parameters.
[0021] The methods include the creation of gain curves and/or
algorithms that model the effects of the process parameters on the
characteristics of the films. For example, a gain curve may be
determined that plots a ratio of the power delivered to heating
elements in different substrate heating zones (i.e., the process
parameter) against variations in the thickness of the film layer.
The gain curve may be used to calculate a power ratio that forms a
film layer with minimized variations from a target thickness.
Additional aspects of embodiments of the methods will now be
described.
Exemplary Methods
[0022] FIG. 1A shows a flowchart that outlines steps in a method of
calculating a process parameter in an epitaxial growth process
according to embodiments of the invention. The method includes
steps to determine a gain curve for a process parameter. This may
include setting the process parameter to a particular value 102,
and measuring a property of interest of the film formed with that
value for the process parameter 104. The process parameter is then
adjusted 106, and the property of interest is measured on a new
film that is formed with the adjusted value of the process
parameter 108. A gain curve may be determined 110, which plots the
film property as a function of the value of the process parameter.
Additional measurements of the property may be taken after further
adjustments of the process parameter to better resolve the gain
curve. For example, measurements of a film property, such as
thickness uniformity, may be plotted according to a plurality of
incremental changes in a process parameter, such as the power ratio
of two substrate heating zones, to determine the gain curve.
[0023] An accurate gain curve permits the tuning of process
parameters to achieve an epitaxial growth film with target
properties without further experimentation. Thus, the method may
include providing a target value for a property of the film 112,
and using the gain curve to calculate a process parameter value for
achieving the target value 114. The target property may be provided
to a computer programmed with the gain curve, and capable of
calculating the process parameter value based on the target value.
Alternatively, an EPI process operator may manually determine the
target value from a plot of the gain curve. In more complex models,
multiple gain curves may be provided to a computer that is operable
to output values for a plurality of process parameters based on one
or more desired target values for film properties.
[0024] For example, the flowchart shown in FIG. 1B has steps for
determining a two-variable gain curve. Embodiments of the method
may include setting of a first and second process parameter 120,
122. A property of the resulting epitaxial film layer is measured
for these values of the process parameter 124, 126. Then, both the
first and second process parameters may be adjusted 128, 130, and
the property of the film layer measured again with the new process
parameter settings 132, 134. A two-parameter gain curve may be
determined 136, which plots the film property as a function of both
process parameters. The steps of adjusting the process parameters
and measuring the effects on the film property may be repeated
multiple times to enhance the resolution of the gain curve.
[0025] The two-parameter gain curve permits the tuning of the
process parameters to achieve an epitaxial growth film with a
target value of the property without further experimentation. Thus,
the method may include providing a target value for a property of
the film 138, and using the gain curve to calculate first and
second process parameter values for achieving the target value 140.
Embodiments with even more complex algorithms and/or gain curves
that are dependent on three or more process parameters are also
contemplated.
[0026] Referring now to FIG. 1C, a flowchart is shown for methods
of setting a process parameter for the formation of an epitaxial
film layer according to additional embodiments of the invention.
The methods include steps to determine effect profiles that relate
the values of one or more process parameters on a concentration
distribution profile of a material in the epitaxial layer. The
steps may include setting the process parameter to a particular
value 160, and measuring the concentration distribution of the
material in the epitaxial layer for that value for the process
parameter 162. The process parameter is then adjusted 164, and the
concentration distribution measured on a new film that is formed
with the adjusted value of the process parameter 166. After
incrementally adjusting the value of the process parameter a number
of times (e.g., increasing the value of the parameter by 5%
increments) an effect profile may be determined 168, which plots
the concentration distribution as a function of the value of the
process parameter. Additional measurements of the property may be
taken after further adjustments of the process parameter to better
resolve the effect profile (e.g. measuring changes in the
concentration distribution for 1% increments in the value of the
process parameter).
[0027] An accurate effect profile permits the tuning of process
parameter to achieve a target concentration profile of a material
in the epitaxial layer without further experimentation. Thus in
this embodiment, the methods include providing a target
concentration profile 170 of a material, such as boron, phosphorus,
arsenic, germanium, indium, gallium, tin, carbon, nitrogen, oxygen,
etc., and using the effect profile to calculate a process parameter
value for achieving the target profile 172. The target
concentration profile may be provided to a computer programmed with
the effect profile, and capable of calculating one or more process
parameter values based on the target profile. Alternatively, an EPI
process operator may manually determine target values from a plot
of the effect profile. In more complex models, multiple effect
profiles may be provided to a computer that is operable to output
values for a plurality of process parameters based on the target
concentration profiles for one or more materials.
Exemplary Systems
[0028] FIGS. 2A-B shows an example of a substrate processing system
according to embodiments of the invention. The processing apparatus
210 shown in FIG. 2A is a deposition reactor and comprises a
deposition chamber 212 having an upper dome 214, a lower dome 216
and a sidewall 218 between the upper and lower domes 214 and 216.
Cooling fluid (not shown) may be circulated through sidewall 218 to
cool o-rings used to seal domes 214 and 216 against sidewall 218.
An upper liner 282 and a lower liner 284 are mounted against the
inside surface of sidewall 218. The upper and lower domes 214 and
216 are made of a transparent material to allow heating light to
pass through into the deposition chamber 212.
[0029] Within the chamber 212 is a flat, circular susceptor 220 for
supporting a wafer in a horizontal position. The susceptor 220
extends transversely across the chamber 212 at the sidewall 218 to
divide the chamber 212 into an upper portion 222 above the
susceptor 220 and a lower portion 224 below the susceptor 220. The
susceptor 220 is mounted on a shaft 226 which extends
perpendicularly downward from the center of the bottom of the
susceptor 220. The shaft 226 is connected to a motor (not shown)
which rotates shaft 226 and thereby rotates the susceptor 220. An
annular preheat ring 228 is connected at its outer periphery to the
inside periphery of lower liner 284 and extends around the
susceptor 220. The pre-heat ring 228 is in the same plane as the
susceptor 220 with the inner edge of the pre-heat ring 228
separated by a gap 402A from the outer edge of the susceptor
220.
[0030] An inlet manifold 230 is positioned in the side of chamber
212 and is adapted to admit gas from a source of gas or gases, such
as tank 141, into the chamber 212. An outlet port 232 is positioned
in the side of chamber 212 diagonally opposite the inlet manifold
and is adapted to exhaust gases from the deposition chamber
212.
[0031] A plurality of high intensity lamps 234 are mounted around
the chamber 212 and direct their light through the upper and lower
domes 214 and 216 onto the susceptor 220 (and preheat ring 228) to
heat the susceptor 220 (and preheat ring 228). Susceptor 220 and
preheat ring 228 are made of a material, such as silicon carbide,
coated graphite which is opaque to the radiation emitted from lamps
234 so that they can be heated by radiation from lamps 234. The
upper and lower domes 214 and 216 are made of a material which is
transparent to the light from the lamps 234, such as clear quartz.
The upper and lower domes 214 and 216 are generally made of quartz
because quartz is transparent to light of both visible and IR
frequencies; it exhibits a relatively high structural strength; and
it is chemically stable in the process environment of the
deposition chamber 212. Although lamps are the preferred means for
heating wafers in deposition chamber 220, other methods may be used
such as resistance heaters and RF inductive heaters. An infrared
temperature sensor 236 such as a pyrometer is mounted below the
lower dome 216 and faces the bottom surface of the susceptor 220
through the lower dome 216. The temperature sensor 236, is used to
monitor the temperature of the susceptor 220 by receiving infra-red
radiation emitted from the susceptor 220 when the susceptor 220 is
heated. A temperature sensor 237 for measuring the temperature of a
wafer may also be included if desired.
[0032] An upper clamping ring 248 extends around the periphery of
the outer surface of the upper dome 214. A lower clamping ring 250
extends around the periphery of the outer surface of the lower dome
216. The upper and lower clamping rings 248 and 250 are secured
together so as to clamp the upper and lower domes 214 and 216 to
the side wall 218.
[0033] Reactor 210 includes a gas inlet manifold 230 for feeding
process gas into chamber 212. Gas inlet manifold 230 includes a
connector cap 238, a baffle 274, an insert plate 279 positioned
within sidewall 218, and a passage 260 formed between upper liner
282 and lower liner 284. Passage 260 is connected to the upper
portion 222 of chamber 212. Process gas from gas cap 238 passes
through baffle 274, insert plate 279 and passage 260 and into the
upper portion 222 of chamber 212.
[0034] Reactor 210 also includes an independent inert gas inlet 262
for feeding an inert purge gas, such as but not limited to,
hydrogen (H.sub.2) and nitrogen (N.sub.2), into the lower portion
224 of deposition chamber 212. As shown in FIG. 2A, inert purge gas
inlet 262 can be integrated into gas inlet manifold 230, if
desired, as long as a physically separate and distinct passage 260
through baffle 274, insert plate 279, and lower liner 284 is
provided for the inert gas, so that the inert purge gas can be
controlled and directed independent of the process gas. Inert purge
gas inlet 262 need not necessarily be integrated or positioned
along with gas inlet manifold 230, and can for example be
positioned on reactor 210 at an angle of 90.degree. from deposition
gas inlet manifold 230.
[0035] Reactor 210 also includes a gas outlet 232. The gas outlet
232 includes an exhaust passage 290 which extends from the upper
chamber portion 222 to the outside diameter of sidewall 218.
Exhaust passage 290 includes an upper passage 292 formed between
upper liner 282 and lower liner 284 and which extends between the
upper chamber portion 222 and the inner diameter of sidewall 218.
Additionally, exhaust passage 290 includes an exhaust channel 294
formed within insert plate 279 positioned within sidewall 218. A
vacuum source, such as a pump (not shown) for creating low or
reduced pressure in chamber 212 is coupled to exhaust channel 294
on the exterior of sidewall 218 by an outlet pipe 233. Thus,
process gas fed into the upper chamber portion 222 is exhausted
through the upper passage 292, through exhaust channel 294 and into
outlet pipe 233.
[0036] The single wafer reactor shown in FIG. 2A is a "cold wall"
reactor. That is, sidewall 218 and upper and lower liners 282 and
284, respectively, are at a substantially lower temperature than
preheat ring 228 and susceptor 220 (and a wafer placed thereon)
during processing. For example, in a process to deposit an
epitaxial silicon film on a wafer, the susceptor and wafer are
heated to a temperature of between 550-1200.degree. C., while the
sidewall (and liners) are at a temperature of about 400-600.degree.
C. The sidewall and liners are at a cooler temperature because they
do not receive direct irradiation from lamps 234 due to reflectors
235, and because cooling fluid is circulated through sidewall
218.
[0037] Gas outlet 232 also includes a vent 296 which extends from
the lower chamber portion 224 through lower liner 284 to exhaust
passage 290. Vent 296 preferably intersects the upper passage 292
of exhaust passage 290 as shown in FIG. 2A. Inert purge gas is
exhausted from the lower chamber portion 224 through vent 296,
through a portion of upper chamber passage 292, through exhaust
channel 294, and into outlet pipe 233. Vent 296 allows for the
direct exhausting of purge gas from the lower chamber portion to
exhaust passage 290.
[0038] According to the present invention, process gas or gases 298
are fed into the upper chamber portion 222 from gas inlet manifold
230. A process gas, according to the present invention, is defined
as a gas or gas mixture which acts to remove, treat, or deposit a
film on a wafer or a substrate placed in chamber 212. According to
the present invention, a process gas comprising HCl and an inert
gas, such as H.sub.2, is used to treat a silicon surface by
removing and smoothing the silicon surface. In an embodiment of the
present invention a process gas is used to deposit a silicon
epitaxial layer on a silicon surface of a wafer placed on susceptor
220 after the silicon surface has been treated. Process gas 298
generally includes a silicon source, such as but not limited to,
monosilane, trichlorosilane, dichlorosilane, and tetrachlorosilane,
methyl-silane, and a dopant gas source, such as but not limited to
phosphine, diborane, germaine, and arsine, among others, as well as
other process gases such as oxygen, methane, ammonia, etc. A
carrier gas, such as H.sub.2, is generally included in the
deposition gas stream. For a process chamber with a volume of
approximately 5 liters, a deposition process gas stream between
35-75 SLM (including carrier gas) is typically fed into the upper
chamber portion 222 to deposit a layer of silicon on a wafer. The
flow of process gas 298 is essentially a laminar flow from inlet
passage 260, across preheat ring 228, across susceptor 220 (and
wafer), across the opposite side of preheat ring 228, and out
exhaust passage 290. The process gas is heated to a deposition or
process temperature by preheat ring 228, susceptor 220, and the
wafer being processed. In a process to deposit an epitaxial silicon
layer on a wafer, the susceptor and preheat ring are heated to a
temperature of between 800.degree. C.-1200.degree. C. A silicon
epitaxial film can be formed at temperatures as low as 550.degree.
C. with silane by using a reduced deposition pressure.
[0039] Additionally, while process gas is fed into the upper
chamber portion, an inert purge gas or gases 299 are fed
independently into the lower chamber portion 224. An inert purge
gas is defined as a gas which is substantially unreactive at
process temperatures with chamber features and wafers placed in
deposition chamber 212. The inert purge gas is heated by preheat
ring 228 and susceptor 220 to essentially the same temperature as
the process gas while in chamber 212. Inert purge gas 299 is fed
into the lower chamber portion 224 at a rate which develops a
positive pressure within lower chamber portion 224 with respect to
the process gas pressure in the upper chamber portion 222. Process
gas 298 is therefore prevented from seeping down through gap 402A
and into the lower chamber portion 224, and depositing on the
backside of susceptor 220.
[0040] FIG. 2B shows a portion of the gas inlet manifold 230 which
supplies gas to the upper zone of the processing chamber. In FIG.
2B the insert plate is shown to be constituted by an inner zone 128
and an outer zone 130. According to this embodiment of the
invention the composition of the process gas which flows into inner
zone 128 can be controlled independently of the composition of the
gas which flows into outer zone 130. In addition, the flow rate of
the gas to either of the two halves 128a-128b of the inner zone 128
can be further controlled independently from one another. This
provides two degrees of control for the gas flow for the purposes
of controlling the composition of the process gas mix over
different zones of the semiconductor wafer.
[0041] Processing apparatus 210 shown in FIG. 2A includes a system
controller 150 which controls various operations of apparatus 210
such as controlling gas flows, substrate temperature, and chamber
pressure. In an embodiment of the present invention the system
controller 150 includes a hard disk drive (memory 152), a floppy
disk drive and a processor 154. The processor contains a single
board computer (SBC), analog and digital input/output boards,
interface boards and stepper motor controller board. Various parts
of processing apparatus 210 conform to the Versa Modular Europeans
(VME) standard which defines board, card cage, and connector
dimensions and types. The VME standard also defines the bus
structure having a 16-bit data bus and 24-bit address bus.
[0042] System controller 150 controls all of the activities of the
apparatus 210. The system controller executes system control
software, which is a computer program stored in a computer-readable
medium such as a memory 152. Preferably, memory 152 is a hard disk
drive, but memory 152 may also be other kinds of memory. The
computer program includes sets of instructions that dictate the
timing, mixture of gases, chamber pressure, chamber temperature,
lamp power levels, susceptor position, and other parameters of a
particular process. Of course, other computer programs such as one
stored on another memory device including, for example, a floppy
disk or another appropriate drive, may also be used to operate
system controller 150. An input/output device 156 such as a CRT
monitor and a keyboard is used to interface between a user and
system controller 150.
[0043] The process for smoothing a silicon surface in accordance
with the present invention can be implemented using a computer
program product which is stored in memory 152 and is executed by
processor 154. The computer program code can be written in any
conventional computer readable programming language, such as, 68000
assembly language, C, C++, Pascal, Fortran, or others. Suitable
program code is entered into a single file, or multiple files,
using a conventional text editor, and stored or embodied in a
computer usable medium, such as a memory system of the computer. If
the entered code text is in a high level language, the code is
compiled, and the resultant compiler code is then linked with an
object code of precompiled windows library routines. To execute the
linked compiled object code, the system user invokes the object
code, causing the computer system to load the code in memory, from
which the CPU reads and executes the code to perform the tasks
identified in the program. Also stored in memory 152 are process
parameters such as process gas flow rates (e.g., H.sub.2 and HCl
flow rates), process temperatures and process pressure necessary to
carry out the smoothing of silicon films in accordance with the
present invention.
Experimental
[0044] A Epi process tuning tool was developed for growing doped
and undoped silicon (Si), doped and undoped silicon-germanium
(SiGe), and/or germanium (Ge) film on substrate wafers (e.g., a 300
mm substrate wafer). The tool was developed from measuring the
effects of process parameters including the ratio of heating lamp
powers for different heating zones on film uniformity. The
experimental results were then entered into a Microsoft Excel
spreadsheet that plotted gain curves showing changes in film
thickness as a function of the lamp power ratios. The Excel
function "solver" was then used to calculate the lamp ratios that
would achieve a target film thickness having high uniformity. The
Epi process was then run with the calculated values of the power
ratios to produce a SiGe film with excellent thickness uniformity
properties with one baseline wafer, and one tuning iteration.
[0045] The Epi growth process conditions for growing the baseline
SiGe film are summarized in Table 1: TABLE-US-00001 TABLE 1 Epi
Process Conditions for Growing Baseline SiGe Film Process Parameter
Value Temperature 800.degree. C. Lower Power Ratio 60% Upper
Inner/Lower Power Ratio 50%/12.5% DCS Flow 100 sccm GeH.sub.4 (1%)
Flow 200 sccm HCl Flow 150 sccm PH.sub.3 (1%) Flow 250 sccm Time
150 sec Pressure 20 Torr H.sub.2 Main 30 slm H.sub.2 Slit 3 slm
Accuset 125/125
[0046] The process conditions for growing the baseline Epi film
were set by integration requirements, and to achieve desired
electrical properties in the film. A DOE was performed to find
values for the baseline process parameters to achieve a selective
SiGe layer 300 .ANG. thick, with a 16% germanium content, and a
resistivity of 300.OMEGA..
[0047] Experimental runs were then conducted with a 300 mm EPI
Centura epitaxial film growth system to determine the effects of
process parameters on the film uniformity. In a series of DOEs, the
process parameters were manipulated around the baseline conditions
to measure the effects on the uniformity of film properties such as
thickness, resistivity, and germanium concentration. Because the
iterative process required a lot of wafers, an attempt was made to
find the most sensitive parameters to effecting the uniformity of
film properties.
[0048] Starting with the baseline process parameters, sensitivity
experiments were performed by making small deviations in each
parameter, and observing which parameters had the greatest effect
on film uniformity. These experiments revealed the accusett for gas
flow distribution, and lamp power adjustments had the greatest
effect on film uniformity. Because the lamp power could be adjusted
with greater resolution, this was the parameter used by the tuning
tool to control film uniformity. It was also observed that film
thickness uniformity was most representative of uniformity of all
the film properties measured, and this was the film property to be
controlled by the tuning tool.
[0049] The lamp power process parameter was defined by the
distribution of lamps around various regions of a substrate that
was rotatable on a susceptor in Epi process chamber. The lamps were
divided into four regions, called the 1) inner and 2) outer zones
of the 3) upper and 4) lower modules. The power supplied to each
region is independently adjustable. For a particular set of
baseline process parameters, like pressure, gas-flows, and
temperature set-point, the lamp power distribution factors for each
region can be adjusted for radiation loss. Adjusting lamp power to
maintain temperature consistency after changes in process
parameters may be assisted by automated control processes like
those described in U.S. Pat. No. 6,164,816 to Aderhold et al,
titled "TUNING A SUBSTRATE TEMPERATURE MEASUREMENT SYSTEM", the
entire contents of which are hereby incorporated by reference for
all purposes.
[0050] Measurements of thickness uniformity were made after small
adjustments to lamp power in each of the regions. The effects were
characterized by subtracting the thickness-line-scan measured
between the adjusted film and a film formed with the baseline
process parameters. The effect of each incremental unit change in
the lamp power level on thickness uniformity provided the data to
determine a gain curve.
[0051] The thickness uniformity data was measured using a 46-point
line scan of thickness across the film. The 46-points were equally
distributed across two perpendicular lines that intersected at the
center of the 300 mm circular substrate wafer. Gain curves were
calculated for changes in thickness uniformity as a function of
adjustments to the power supplied to each lamp region. The
parameters were considered independent, and each parameter had an
additive effect on the uniformity of the film thickness. Gain
curves plotting the effects of parameter adjustments on film
thickness uniformity were entered into a Microsoft Excel
spreadsheet, and used to predict a 46-point thickness distribution
based on the process parameter settings.
[0052] The parameters were calculated to produce a minimal standard
deviation in the thickness uniformity using the Excel spreadsheet
function "solver". For small changes, the variation in the system
is approximated as linear, so linear extrapolation from an input
measurement was used to predict the direction of a parameter change
that will improve the film thickness uniformity. Non-linear
extrapolation models may also be used for predicting parameter
settings that minimize variations in film thickness.
[0053] The number of process parameters calculated by the tuning
tool was reduced from four to two by looking at the ratio of inner
to outer zone lamp power ratio (first parameter), and the upper to
lower lamp power ratio (second parameter). With the baseline film
already made, three additional wafers were processed and film
thicknesses measured. Wafer #1 was run with the same parameters
except a 2% higher inner to outer lamp power ratio, and wafer #2
ran with baseline parameters, except for a 2% higher upper to lower
lamp power ratio. FIGS. 3A and 3B show changes in the film
thickness profiles caused by changes in each process parameter.
[0054] In FIG. 3A, a thickness profile is shown for a 2% increase
from baseline in the ratio of lamp power between the inner and
outer lamp zones. The baseline thickness data was subtracted from
the wafer #1 thickness data, and normalized by division with 2%. To
remove the slope in the data across the radius, a folding operation
was used, and the data was smoothed to get the line shown. In FIG.
3B, a thickness profile is shown for a 2% increase in baseline in
the ratio of lamp power between the lower and upper lamp modules.
The baseline thickness data was subtracted from the wafer #2
thickness data, and also normalized by division with 2%. A similar
folding and smoothing operation was performed to get the line
shown. Overall temperature sensitivity was measured at 5.6 .ANG./K.
The data showing the effects of the two process parameters on the
uniformity of film thickness were used to determine two gain
curves, one for each parameter.
[0055] The gain curves were incorporated into the tuning tool, and
comparative experiments were run for tuning the two process
parameters manually and with the tool. FIG. 4 shows the thickness
uniformity results from tuning the process parameters. As shown,
the thickness variation was 1.7% with an inner to outer power ratio
of 52% (Wafer 303WB256), and 1.9% with an inner to outer ratio of
54% (Wafer 303WB259). In summary, with manual tuning the lowest
variation in film thickness achieved was about 1.7%. The high
thickness variation (i.e., low thickness uniformity) was believed
to be caused by interdependencies between lamp power settings that
were not well understood. While changes the inner to outer lamp
power ratio moved the thickness profile in a way predicted by the
gain curve (see FIG. 3A), it did not improve the overall smoothness
of the feature in the center of the wafer.
[0056] FIG. 5 shows the thickness uniformity results from tuning
the process parameters with the aid of the Epi process tuning tool.
The tuning tool factors the interdependence of the lower to upper
and inner to outer ratios of lamp power when calculating the tuning
values for both process parameters. The tuning tool output an
increase in the upper to lower lamp power ratio by 12%, while
decreasing the inner to outer ratio by 1%. The predicted thickness
uniformity of 1.3% calculated by the tool matched the actual
thickness uniformity achieved in one run (wafer 303WB362). This is
down from 1.8% thickness uniformity for the wafer produced with the
baseline starting parameters (Wafer 303WB350). Thus, compared with
manual tuning, tuning process parameters with the help of the Epi
process tuning tool shows significant improvements in thickness
uniformity after fewer tuning iterations.
[0057] Experiments can also be conducted to develop an effects
profile to help achieve target concentration distribution of a
dopant. One target profile calls for a substantially uniform
concentration of boron of about 1.times.10.sup.20 atoms/cm.sup.2
across a 300 .ANG. thick SiGe epitaxial layer (Ge concentration of
20%). Measurements of the boron concentration distribution can be
made after small adjustments to process parameters like the flow
rate of a diborane process gas. The measured boron concentration
distribution data can then be used to develop an effects profile
that relates the effect of the diborane flow rate value to the
concentration distribution profile formed in the epitaxial layer.
The effects profile may then be used to find values for the
diborane flow rate that give the minimum deviation from a uniform
concentration distribution profile of boron atoms in the epitaxial
layer.
[0058] Having described several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Additionally, a number
of well known processes and elements have not been described in
order to avoid unnecessarily obscuring the present invention.
Accordingly, the above description should not be taken as limiting
the scope of the invention.
[0059] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limits of that range is also specifically disclosed. Each
smaller range between any stated value or intervening value in a
stated range and any other stated or intervening value in that
stated range is encompassed. The upper and lower limits of these
smaller ranges may independently be included or excluded in the
range, and each range where either, neither or both limits are
included in the smaller ranges is also encompassed within the
invention, subject to any specifically excluded limit in the stated
range. Where the stated range includes one or both of the limits,
ranges excluding either or both of those included limits are also
included.
[0060] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a process" includes a plurality of such processes and reference to
"the electrode" includes reference to one or more electrodes and
equivalents thereof known to those skilled in the art, and so
forth.
[0061] Also, the words "comprise," "comprising," "include,"
"including," and "includes" when used in this specification and in
the following claims are intended to specify the presence of stated
features, integers, components, or steps, but they do not preclude
the presence or addition of one or more other features, integers,
components, steps, acts, or groups.
* * * * *